Originally Posted by
109jb
From my perspective as a hobby user.
Price and capability are the biggest concerns for me as a hobby user. Price is of great concern because this is a hobby for me and I don't make any money with my machines. I only have so much money to spend on this hobby so again price is very important. Capability is important because I tend to make parts out of steel a lot and need rigidity. Work envelope is also important and leads back to capability.
As far as work envelope, your work envelope is much too small for my taste. You mention an RF 45 in your post, but even the travel specs for your "large" machine are less than an RF45 type machine. My RF45 clone has 22" X travel, 8.5" Y travel, and 13.75" Z travel. The travels you mention for the "large" machine are 13.8, 8.3, and 11.8 respectively. I can achieve those travels with my Grizzly G0704 which I would not consider "large" by any means.
I recently bought a RF45 type machine with VFD controlled spindle for $2500 which included all taxes and delivery. Certainly the linear rails and ballscrews already installed is worth something, but if the price point isn't at least close to what an RF45 type machine is then I personally would not even consider it and it should be at least as rigid.
As far as the linear rails is concerned, I personally think people put too much stock in them. Although they certainly have benefits, I have never had any problem with dovetails for my use and I doubt that most people really require them even if they have them on a metal cutting machine. Linear rails for me isn't a have to have by any stretch.
I currently have my RF45 machine running under CNC in the X and Y axes and will have the z running soon. With all of the parts to put ballscrews, mounts, etc on, including all electronics and NEMA 34 closed loop steppers, I will be right at about $4000 when completed. If the machine you are proposing can't achieve the work envelope, rigidity and price then I personally would not consider it.
If it were a money making endeavor where I was making money on the parts coming out of the machine, I would not even consider a converted machine and would go to a turn key machine.
Just my 2 cents worth.